When combustion occurs in an environment with excess oxygen, peak combustion temperatures increase which leads to the formation of unwanted emissions, such as oxides of nitrogen (NOx). This problem is aggravated through the use of turbocharger machinery operable to increase the mass of fresh air flow, and hence increase the concentrations of oxygen and nitrogen present in the combustion chamber when temperatures are high during or after the combustion event.
One known technique for reducing unwanted emissions such as NOx involves introducing chemically inert gases into the fresh air flow stream for subsequent combustion. By thusly reducing the oxygen concentration of the resulting charge to be combusted, the fuel burns slower and peak combustion temperatures are accordingly reduced, thereby lowering the production of NOx. In an internal combustion engine environment, such chemically inert gases are readily abundant in the form of exhaust gases, and one known method for achieving the foregoing result is through the use of a so-called Exhaust Gas Recirculation (EGR) system operable to selectively introduce (i.e., recirculate) exhaust gas from the exhaust manifold into the fresh air stream flowing to the intake manifold via an EGR conduit coupled between the intake and exhaust manifolds. Through the use of an on-board microprocessor, control of an EGR valve disposed in-line with the EGR conduit is typically accomplished as a function of information supplied by a number of engine operational sensors to thereby control EGR flow.
It is desirable in such systems to monitor a pressure differential across a flow restriction mechanism disposed in-line with the EGR conduit via a differential or delta pressure sensor arrangement, wherein the flow restriction mechanism may be the EGR valve itself or another known flow restriction arrangement. It is further desirable in such systems to monitor the operation of the delta pressure sensor to insure that the information provided by this sensor is reliable. What is therefore needed is a system for monitoring delta pressure sensor operation and diagnosing delta pressure sensor faults or failure conditions as they may occur.